stupid question

Hi friends,
Im new at this site, but Im an old known in Argentina aviation forums.
My question is, actually, quite simple:
how come nobody sees the need for a simple, light, singel engined, modern figther? Does anyone did the math on how many Mirage IIIs, Mirage Vs, Mig21s, old sukois, and similars still flying arround the world? and, even worst, how many were retired and not replaced?
I think it would be a good idea to reopen Mirage 2000 line, but I think French mangmet still thinking it would canibalize Rafales sales (wich hasnt been so great anyway).
India maybe doe not the knowledge or cash to pull off Tejas program, but I think they were in the right direction.
Just imagine the sales of a brand new Mirage 2000, with open BUS architecture for avionics integration (Elbit, Thales, Irbis, etc) and a rebumped turbofan…. I think they maybe lost millions in Rafale exports, but earn billions in Mirage 2000 “NG” sales….
Saab Gripen is the aircraft more in line with my idea, even when it has a lot of “closed components”. Now Brazil has signed a deal, for 36 of them…. lets see how far they go in customization. They could take a lot of sales, specially in South america.
anyone with me?